Fluid-dispenser pumps are well known in the prior art. The present invention relates more particularly to pumps in which the return spring of the pump is not in contact with the fluid dispensed by the pump. The spring is therefore disposed in a chamber inside the pump body, which chamber is isolated from the fluid, but contains air. During actuation of the pump, the moving element of the pump which co-operates with the spring is displaced, thereby compressing the spring, and the presence of the air can pose a problem with regard to the ease of use or the reliability of the pump.